1. Field of the Invention
Aspects of the present invention relate to a polymer battery pack and, more particularly, to a polymer battery pack capable of improving external strength and increasing capacity and a manufacturing method of the polymer battery pack.
2. Description of the Related Art
Generally, a polymer battery pack includes a core pack which is a protection circuit member connected to a bare cell having a form of a pouch and a plastic case in which the core pack is inserted and of which all seams are ultrasonically welded. Here, the bare cell having the form of the pouch is a lithium polymer battery having a structure in which an electrode assembly including a cathode, a separator, an anode, and polymer electrolyte is accommodated into the pouch made of cast polypropylene (CPP), aluminum, nylon, or polyethylene terephthalate (PET). The polymer battery pack or a lithium polymer battery is so named to differentiate it from a lithium ion battery pack or a lithium ion battery which uses a liquid electrolyte.
However, the lithium polymer battery pack may be easily damaged by external forces to decrease reliability of the battery pack, since the pouch constituting the bare cell and a plastic case wrapping the pouch are weak. In other words, aluminum used for the pouch is in a form of a foil and the plastic case wrapping the pouch is thin, so that the pouch and the plastic case may be easily deformed and easily pierced by a sharp instrument such as a nail or a needle. When the polymer battery pack is deformed or pierced by a sharp instrument, a smoke, a flame, or an explosion may occur due to an internal short.
In addition, along seams of the plastic case in the polymer battery pack, a rib space is required for ultrasonic welding the plastic case, and the space occupies at least 0.8 mm or more. Accordingly, a size of the core pack, which is the bare cell, inserted into the polymer battery pack is decreased, and this results in a decrease in the capacity of the battery pack. In other words, the size of the core pack which can be inserted into the plastic case is comparatively very small compared to the size of the plastic case, so that the core pack of high capacity cannot be inserted into the plastic case. In practice, a conventional polymer battery pack cannot accommodate the core pack of approximately 680 mAh capacity or more.